UNIVERSITI PUTRA MALAYSIA
DESIGN OF DATA TRANSCEIVER USING DIFFERENTIAL QUATERNARY PHASE SHIFT KEYING
(DQPSK) MODULATION TECHNIQUE
CHUAH KHAR-YEE
FK 1996 4
DESIGN OF DATA TRANSCEIVER USING
DIFFERENTIAL QUATERNARY PHASE SHIFT KEYING
(DQPSK) �IODULATION TECHNIQUE
CHUAH KHAR-YEE
MASTER OF SCIENCE UNIVERSITI PERTANIAN MALA YSIA
1996
DESIGN OF DATA TRANSCEIVER USING
DIFFERENTIAL QUATERNARY PHASE SHIFT KEYING (DQPSK) MODULATION TECHNIQUE
By
CHUAH KHAR-YEE
Thesis Submitted in Partial FulfiUment of the Requirements for the Degree of Master of Science in
the Faculty of Enaineering,
U niveniti Pertanian Malaysia Selanlor, MaiaysiL
1996
ACKNOWLEDGMENTS
I would like to take this opportunity to express my deep appreciation to Dr.
Borhanuddin Mohd. Ali and Dr. Ahmad Zaki Mohd. Sallch for their constant
guidance, encouragement, and strong support throughout the research work. I would
also like to express my thanks to Dr. Malay Raj Mukeljee and Puan Ratna Kalos
Zakiah Shabuddin for serving as a member of the supervisory committee.
I want to thank my company, Northern Telecom (M) Sdn. Bhd. for granting
the study leave to complete my study. I also want to thank my colleagues, Mr. Teoh
Geok Cheng, Mr. Zaidi Shamsuddin, Ms. Lian Yean-Thow and Ms. Onn Swee-Cheng,
who have constantly given support during my study.
A special thank goes to my best friends : Saw Leng-Pob, Ooi Hock-Eng, Tan
Chin-Hong and Tan Chow-Hwa for their help and encouragement. A special thank
also goes to Mr Choo Wai-Heng (EEsof, Application Engineer), for his constant
guidance and strong support throughout the research work.
Finally, I would like to acknowledge the love, financial support and
encouragement to me by my mother Lee Got-Cheng, my sisters Khar-Ling, Khar-Le
and Khar-Eng. Last but not least, I would like to thank my girl friend, Ng Sze-Yun for
her patience, help and moral support.
ii
TABLE OF CONTENTS
Page
ACKN'OWLEDGMENTS .......................................................... ............. 11
UST OF TABLES .................................................................................. Vl
LIST OF FIGURES ............... ....... ......... ........ ..... ........... ........................... Vll
TERMS AND ABBREVIATIONS .................................... ...................... IX
ABSTRACf ............................................................. ............................... Xl
ABSTRAI{ ............................................................................ ..................... Xlll
CHAPTER
I INTRODUcnON .............................................. ................... 1
Introduction ......... ............ ............................... .................... ..... ....... 1
Limitation in Communication ........................................................ 4
Cordless Telecommunication second Generation (CT2) ...... ............. 5
Objective of the Study ......................................... ............................ 7
The Goal of Study and Organization of Dissertation ................... 9
n LITERATURE REVIEW AND BACKGROUND THEORY .. ... 10
Noise In Communication Systems ............................... . ............... 10
Digital Modulation Techniques .................................................... 12
Modulation Performances and Comparison ................................... 17
iii
III
IV
Perfonnance Comparison
Bandwidth Comparison
Page
17
18
BPSIHZ Comparison .. ... ........ ... .. ... ....... .... .. ..... ........ ..... 1 �
Quaternary Phase Shift Keying . .......... .. ...... .. .... ....... .... .. ... ...... 2 1
QPSK Modulator .. ......... .... .................................................. 21
QPSK Demodulator................................................................ 26
Differential Quaternary Phase Shift Keying ... .... ........... . .... ...... .. .... . 29
DQPSK Modulator ... ................... ... ... .... ..... ... .... .. .... .. ...... ....... 30
OQPSK Demodulator .... ..... ..... .......... .................................... 32
SYSTEM DESIGN AND PLANNING 35
Introduction ........................................ ....................... ............ . . . . . . . 35
RF System Design Process
RF Transmitter
36
39
Space Propagation .. ..... ... ... ... ... .... ......... ... ............... . ... ..... ....... . . . . 44 RF Receiver ... ................ . :............................................................ 46
TEST SET-UP AND ANAL YSIS 52
Introduction . ...... ... .......... .. ...... .... ........... .......... .... .. ....... ... .. ......... . 52
Set-up of System Test Bench 55
V SIMULATION RESULTS AND DISCUSSION . .. ... .... .. . 61
Introduction .... ..... .... .................. .... .... ....... .... ........ ... ..... ..... .. ... . ....... 61
Systems Comparison
Characteristics and Performance of I-GHz Transceiver
63
69
iv
Page
VI SUMMARY AND CONCLUSION . . . ................... . . . . . . . 78
Future Study . . ..... . ........................................................ . ................... 80
REFERENCES .................... . . ............... . . . ................ . . .................. . .. . . . . 8 1
v
LIST OF TABLES
Table Page
1 Key Parameters for Cordless Telecommunication 2nd Generation (CT2) .... ....... ............ .................................... .................. 6
2 Design Specification ...................................................................... 8
3 Four Possible Forms of QPSK Signal ........ ...... ........ .......................... 23
4 Output of PDI and PDQ ................................................................. 28
s Differential Encoding of Input (I, Q) Dibit 31
6 Summary of Test Pins for the Transceiver ................. ..................... 55
7 Summary of the Key Parameters for CT2 and DQPSK System ....... 75
vi
LIST OF FIGURES
Figure Page
1 BASK Wavefonn Where m = Y2 .... ............ ............ .......................... 13
2
3
4
Wavefonn of On-Off Keying
BFSK Wavefonn for 1010 Bit String
Perfonnance ofMFSK and MPSK
14
15
18
5 Ideal Bandwidth-per-bit-rate Comparison for Various MPSK and MFSK Modulation Techniques ............ ....................... 19
6 BPSIHz versus FJNo for Various Modulation Techniques ........... 20
7 Block Diagram of QPSK Modulator ........................................... 22
8 Constellation Diagram of QPSK .... ...... ....... .......... ............ ........ ....... 23
9 Wavefonn of dk(t) = 11000111, dI(t) and �(t) ............................. 25
10 SQPSK Signal of dk(t) = 11000111 ................................................ 25
11 Block Diagram of QPSK Demodulator
12 Carrier Recovery System for QPSK Demodulator
13 Clock Itecovery Circuit for Bit Timing Recovery for QPSK
26
28
Demodulator ... ..... .......... ............ ........................... .............. .......... 29
14 Block Diagram of DQPSK Modulator 32
15 DQPSK Demodulator Network ...................................... . .............. 34
16 An RF System Design Process Flow Chart ................................... 38
17 DQPSK Transceiver Block 40
18 Frequency-domain Representation Of Rai3ed Cosine Filter ........ 42
19 Time-domain Representation of Raised Cosine Filter 42
20 DQPSK Receiver Block ...... ........................ ............................. 48
21 DQPSK Transceiver Block
22 Test Points and White Noise Generator In Transceiver
51
53
vii
Page
23 Test Bench for Transceiver .......................................................... 56
24 Probability of Error (P e> Comparisons for FSK and DQPSK 62
25 P e Versus Eb"No With Fixed Tx Power [Tx_ PWR] Set At +35 dBm ................................... ........................................ 63
26 P e Versus Eb"No With Fixed Rx Power [Rx_ PWR] Set At -60 dBm ............. .................................................................... 65
27 P e Versus Eb"No With Various Distance for 1_ GH and 5_ GHz Transceivers ...... . ...... . . ......... . . ... . . . . ..... .... . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
28 P e Versus Distance With Various EtlNo
29 P e Versus EtlNo With Various Rx Power [Rx_ PWR]
68
For I_ GIl Transceivers ................................................................ 70
30 P e Versus EtlNo for +35dBm Tx power [Tx_ PWR] With Various Throughput ...................................................................... 71
31 P e Versus EtlNo for 1_ GHz Transceiver With M 32 P e Versus M for 1_ GHz Transceiver With EtlNo
73
74
viii
LIST OF ABBREVIATIONS
AGC Automatic Gain Control
ASK Amplitude Shift Keying
BASK Binary ASK
BER Bit Error Rate
BFSK BinaryFSK
BPSK BinaryPSK
BS Base Station
CDMA Code Division Multiple Access
CT Cordless Telephone
CT2 Cordless Telephone 2nd Generation
DECT Digital European Cordless Communication
DQPSK Differential QPSK
FDD Frequency Division Duplex
FDMA Frequency Division Multiple Access
FM Frequency Modulation
FSK Frequency Shift Keying
GMSK Gaussiam Minimum Shift Keying
GSM Global System for Mobile Communication
IF Intermediate Frequency
lSI Intersymbollnterference
lTV International Telecommunication Union
LNA Low Noise Amplifier
LO Local Oscillator
IX
L02 Second Local Oscillator
LOS Line-of-Sight
MDS Minimum Detectable Signal
NF Noise Figure
NRZ Non-Return to Zero
PA Power Amplifier
PM Phase Modulation
PSI( Phase Shift Keying
QAM Quadrature Amplitude Modulation
QPSI( Quaternary Phase Shift Keying
RF Fladio Frequency
SAW Surface Acoustic Wave
SNR Signal-to-Noise Ration
TDMA Time Division Multiple Access
UHF Ultra High Frequency
VCO Voltage Controlled Oscillator
Abstract of thesis submitted to the Senate of Universiti Pertanian Malaysia in fulfillment of the requirements for the Degree of Master of Science.
DESIGN OF DATA TRANSCEIVER USING DIFFERENTIAL QUA TERNARY PHASE SHIFT KEYING (DQPSK)
MODULA nON TECHNIQUE
By
CHUAH KHAR-YEE
November 1996
Chairman : Dr. Borhanuddin Mohd. Ali
Faculty : Engineering
There are few factors that contributes to the commercial failure of the
Cordless Telecommunication 2nd Generation (CT2) system. Amongst those factors
are the limitations and inefficiency of the system, such as cell size, bit-error-rate,
throughput and bandwidth efficiency. The aim of this study is therefore to propose a
modulation technique that could potentially overcome some of the above mentioned
limitations.
To model the system, a reliable data transceiver using Differential Quaternary
Phase Shift Keying (DQPSK) modulation technique was designed and simulated using
HP-EESof Microwave System Simulator called OmniSys. Two frequency
spectrum, namel� I-GHz and 5-GHz, which are commonly used in cellular phones
and satellite communications respectively, have been selected for analysis. However,
because of the higher propagation path loss for 5-GHz, only the I-GHz system was
selected for further investigation in this thesis, as a proposed frequency to improve the
CT2 system.
Simulations of the DQPSK transceiver at I-GHz have shown that bit-error
rate (BER) of 10-6 or better could be achieved compared to 10-3 in CT2. This is
suitable for data transceiver with a minimum receive power (Rx_PWR) of -60dBm.
The coverage also improved from 200 meters (maximum radius for CT2) to 1250
meters with acceptable transmit power «35dBm).
The simulation also showed that the throughput (TP> of 120 Kbitls can be
achieved compared to 72 Kbitls for CT2 system and the bandwidth efficiency can be
improved from 0.72 bitIHz for CT2 system to 1.46 bitIHz for the proposed system.
Thus, from these simulation results, the aim of proposing a modulation
technique to improve CT2 system has been achieved. The performance of the reliable
data transceiver using DQPSK modulation technique operating at I-GHz has found to
be satisfactory.
xii
Abstrak tesis yang dikemukakan kepada Senat Universiti Pertanian Malaysia bagi memenuhi keperluan untuk Ijazah Master Sains.
REKABENTUK DATA PEMANCAR-PENERIMA DENGAN MENGGUNAKAN TEKNIK MODULASI
DIFFERENTIAL QUATERNARY PHASE SHIFT KEYING (DQPSK)
Qleh
CHUAH KHAR-YEE
November 1996
PeDlerusi : Dr. Borhanuddin Mohd. Ali Fakulti : Kejuruteraan
Terdapat beberapa faktor yang menyumbang kepada kegagalan
Telekomunikasi Mudahalih Generasi Kedua (Cordless Telecommunication 2nd
Generation, CT2), namun faktor-faktor utama adalah akibat had-had serta
ketidakberkesanan sistem, seperti saiz sel. kadar ralat bit, "throughput" dan
kekesanan lebarjalur. Tujuan kajian ini adalah untuk mencadangkan satu teknik
modulasi yang berpotensi untuk mengatasi had-had seperti yang dihuraikan diatas.
Untuk memodelkan sistem tersebut, satu pemancar-penerima (transceiver)
data Differential Quaternary Phase Shift Keying (DQPSK) telah direka dan
mi
disimulasikan menggunakan Penyelaku Sistem Gelombang MUcro HP-EESof (HP
EESofMicrowave System Simulator) yang dekenali sebagai OmniSys. Dalam proses
rekabentuk, 2 jalur spektrum frekuensi iaitu 1-GHz dan 5-GHz yang lazim digunakan
dalam telefon bimbit dan komunikasi satelit, telah dipilih untuk analisis dalam tesis ini.
Tetapi, olehkerana sistem S-GHz menghadapi kehilangan perambatan yang tinggi,
maka frekuensi 1-GHz telah dipilih untuk kajian selanjutnya dalam tesis ini sebagai
satu frekuensi yang sesuai untuk memajukan sistem CT2.
Hasil simulasi bagi sistem 1-GHz telah menunjukkan bahawa kadar ralat bit
(BER) 10-6 atau lebih baik boleh diperolehi berbanding dengan 10-3 dalam CT2. Ini adalah sesuai untuk pemancar-penerima data dengan kuasa penerima minimum
(Rx _ PWR) pada -60dBm. Kawasan liputan juga dapat dipertingkatkan dari 200
meter radius maksima (untuk CT2) kepada 1250 meter· dengan kuasa pemancar
sederhana «35 dBm).
Simulasi juga menunjukkan bahawa throughput (T� pada 120 kbitls boleh
dicapai berbanding dengan 72 kbitls bagi sistem CT2 dan kekesanan lebaIjalur boleh
dipertingkatkan dari 0.72 bitIHz bagi sistem CT2 kepada 1.46 bitIHz bagi pemancar
penerima data menggunakan teknik modulasi DQPSK yang dicadangkan.
Oleh itu berdasarkan kepada analisi hasil simulasi, tujuan utama dalam
mencadangkan satu teknik modulasi untuk ml!mperbaiki sistem CT2 telah tercapai.
Pencapaian bagi data pemancar-penerima yang menyakinkan dengan menggunakan
teknik modulasi DQPSK yang beroperasi pada 1-GHz didapati juga adalah
memuaskan.
xiv
CHAPTER I
INTRODUCTION
Communication engineers have long recognized the need to maximize the
usage of expensive communication equipments and effective use of available
bandwidth to minimize the blocking probabilities without sacrificing the quality and
the performance of the systems (Tobagi et al., 1978; Kahn at el., 1978).
There are two main multiplexing techniques, partitioning the channel into
separate non-overlapping frequency sub-bands or by scheduling each user's
transmission to occur in short non-overlapping intervals in time. The first technique is
called Frequency Division Multiple Access (FDMA). Each user has access to a
dedicated portion of the channel at all times. In the second case, known as Time
Division Multiple Access (TDMA), each u� has access to the whole channel for only
a fraction of the time.
To achieve effective use of available bandwidth, channel (frequency) reuse
after a small distance can be achieved in FDMA system by implementing a micro
1
2
cellular structure with a cell size as small as possible. This technique has been
adapted in Cordless Telephone Second (CT2) generation standard (Kahn et al., 1978;
Tan et al., 1993; Bersekas and Gallager, 1992). Transmissions using FDMA with
Frequency Division Duplex (FDD) are widely used on first generation analogue
cellular mobile radio systems. For FDMAlFDD technique, there is a group of n
contiguous sub-bands occupying a bandwidth W Hz for forward or down-link radio
transmissions from a Base Station (BS) to its Mobile Station� (MS), and a similar
group of n sub-bands for the reverse or up-link transmissions from the MSs to their
BS. For cordless telecommunication (CT), FDMAlTDD is used. In this arrangement,
only one band is provided for mobile transmission, so the time frame structure is used
allowing transmission to be done during one half of the frame while the other half of
the frame is available to receive signal (Steele, 1995).
The efficiency of TDMA system can be improved by sending data packet by
packet to improve the throughput and blocking of the system. Packet radio is a
technology that extends the application of packet switching (Kahn et al., 1978;
Bersekas and Gallager, 1992). Studies have shown that transmitting very long
messages as units in a subnet is harmful in several ways, including delay, buffer
management, ernr and congestion control. Thus, message represented by long string
of bits can be broken into shorter bit string caJed packet. A packet of information
includes all the addressing and controlling infonnation based on X.25 standard from
International Telecommunication Union (ITU). Comprehensive introduction to
switching and packet format can be found in many textbooks including Bersekas and
Gallager [1992], Cuthbert and Sapanel [1993] and Stallings [1990].
The rapid development in packet radio has been greatly stimulated by the need
to provide mobile data communication equipments. Packet radio offers a highly
3
efficient way of using a multiple access channt"l, particularly with a large number of
mobile subscribers and users with bursty traffic. In general, packet radio network
services and capabilities include transparency, area coverage and connectivity,
mobility, throughput and low delay, rapid and conveni�nt deployment, error control,
routing option and addressing option (Kahn et aI., 1978).
Recently, with the growth of digital cor.ununication equipments, notebook
computers and the explosive increase of travel and time management have increased
the need of mobile digital communications. Because frequency spectrum suitable for
mobile communication is limited, therefore there is a need for communication
engineers to pack as many bits as possible into the allocated frequency spectrum. To
further maximize the bandwidth efficiency and improve the use of communication
equi!)ments, the combination of both FDMA and TDMA multiplex techniques have
been widely used as well. The approach where TDMAlFDMA operates with FDD is
employed by the Global System for Mobile Communication (GSM) and the Digital
European Cordless Telecommunication (DECT) networks uses TDMAffDDIFDMA
approach (Yamauchi, 1994; Jagoda and Villepin, 1993).
Beside FDMA and TDMA, Code Division Multiple Access (COMA) is
another method that allows multiple users to access the mobile radio communication
network. The system allows each user to use the bandwidth like FDMA and for the
complete duration of the call like TDMA. Although CDMA has been well understood
for a long time, its use in cellular radio had been avoided mainly due to the problem
associated with the power control. Other problems sited were whether there are
sufficient codes available for larger number of mobile users, and difficulties of
synchronization. Comprehensive introduction to switching and packet format can be
4
found in many text books including Steele [ 1995] and, Pahlavan and Levesque
[ 1995}.
Limitation in Communication
Since the frequency spectrum suitable for mobile communication is so limited,
a lot of studies have also been carried out in the area of data compression techniques
to reduce the number of bits required to send a given message, better modulation
techniques to improve bit rate per unit bandwidth hence to maximize the use of
frequency spectrum.
The goals (Sklar, 1988) of the communication designer to use the frequency
spectrum (bandwidth) effectively are clear, and they are�
• to maximize transmission bit rate, BR
• to minimize probability of bit error, PB
• to minimize required system bandwidtb, BW
• to minimize required power, or equivalently to minimize required bit energy to
noise power spectrum density BtlNo
• to maximize system utilization, or equi valently to provide reliable service for a
maximize number of users, Nu
However there are several constraints and theoretica11imitations such as�
6
T�lble 1 Key Parameters for Cordless Telecommunication 2nd Generation
Parameters Frequency band 800 - 1000 MHz Multiple Access FDMA Duplex TDD
Carrier SpacinK 100 kHz Modulation GMSK
Bit Rate 72 kbitls
Maximum Coverage 200 meters
Bit Error Rate (BER) @ -94dBm 10-3
Hand-otT No
There are few factors that contributed to the failure of CT2 system� technical
issue, marketing and commercial errors. Technical issue was attributable to the delay
of formulating the specification. Amendments to the 1989 standard were not
published until the next year, thereby delaying product development and marketing
(Jagoda and ViUepin. 1993). However, the failure ofCT2 system were mainly due to
the following factors (pahlavan, and Levesque, 1995);
• with a channel spacing of 100 kHz. the bandwidth efficiency of CT2 is only
0.72 bitlsecIHz. which is very inefficient.
7
• the system was designed mainly for voice (BER of 10-3). With the growth of
notebook computer, transceiver with minimum BER of <10-6 is required to
send data.
• the system allows to initiate but not receive calls and the system cannot
provide call handoff to another base statbn.
• the coverage is too small, therefore call must be made next to base station.
Due to small coverage, users need to find where Telepoints are before making
call.
Objective of the Study
The main purpose of this thesis is to design a Reliable Data Transceiver Using
Differential Quaternary Phase Shift Keying (DQPSK) Modulation Technique that
could potentially solve the frequency bandwidth limitation in digital portable
communication. Based on Shannon's theorem (Chapter 2), 16-QAM (16-Quadrature
Amplitude Modulation) can provide higher bit rate per bandwidth than DQPSK,
however, the additional complexity of 16-QAM may cancel the benefits associated
with this observation. Due to its advantages, DQPSK still find wide application in
high speed carrier modulation data transmission systems.
In this investigation, the modulation technique, throughput, coverage and
error performance (Bit Error Rate, BER) of a hand held transceiver have been studied
8
using an available microwave simulation softwue. To investigate the system, a few
parameters (Table 2) are set for the project.
Table 2 Design Specification for Reliable Data Transceiver
T�eted
1. Modulation Technique DQPSK
2. Carrier Fr�ue� F� 1000 MHz 3. Throughput, Tn � 100 KBit / sec
4. Coverage, Radius � 1000 meters
5. Receive Sensitivity � -60 dBm
6. Error Performance, p .. � 10-6 @ E,,/Nn � 20 dB
For a fair comparison, the carrier frequency for !he proposed reliable data transceiver
was set at 1000 MHz. To ensure the system has higher throughput compared to CT2
(72 Kbitls), the minimum throughput for the system was predetermined at 100 Kbitls.
For coverage, 1000 meters (radius) was selected since this is the normal cell size for
high frequency cellular. To design a reliable data transceiver, � -60 dBm and � 10-6
were predetermined for receive sensitivity and error performance (P J respectively.
9
The Goal of Study and Organization of Dissertation
The overall goal of the study is to propose a system that could potentially
overcome the limitations of the CT2 system. Several simulation studies using HPEESof Microwave System Simulator called OmniSys were conducted to validate the
proposed �ystem.
In this report, first a brief literature review and background theory are
presented in Chapter 2. Overall transceiver designs using OmniSys are given in
Chapter 3, ",bile Chapter 4 discusses how the system test bench is assembled to
analyze the performance of the transceiver. The simulation results and discussion is
presented in Chapter 5, and summary and conclusion of this thesis in this area of study
will be given in Chapter 6.
CHAPTER II
LITERATURE REVIEW
Noise in Communication Systems
Noise, in the broadest sense, can be defined as any unwanted disturbance that
obscures or interferes with a desired signal, ana make it more difficult to extract the
information (Motchenbacher, and Connelly, 1993). In general noise is a totally
random signal and it consists of all frequency components that are random in both
amplitude and phase therefore it cannot be predicted exactly, nor can it be totally
eliminated, but it can be manipulated and its effects minimized. If the instantaneous
amplitude of noise can be predicted, noise would not be a problem in electrical system
anymore. Although noise cannot be predicted, but much noise has a Gaussian or
normal distribution of instantaneous amplitude with time.
Noise is the major factor that limits the performance of communication
systems (Freeman, 1991). In communication systems, noise can be grouped into
4 categories; thermal noise, inter-modulation noise, crosstalk and impulse noise.
10